If electricity is being used to generate heat (for a house, hot tub, etc), and that heat happens to be generated by a bitcoin miner, is it more or less wasteful than only using the electricity to generate heat?
That's fine, provided you weren't going to heat it with a heat pump before you decided to use a Bitcoin miner. I suppose there's also a slight environmental cost in producing a Bitcoin miner vs producing a heating coil but I'm going to assume that's negligible.
Depends if they are wintering inside or in the hot tub.